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Researchers at Fudan University in Shanghai, China are proposing a method which could lead to the first soft, tunable metamaterial, the key ingredient in building an invisibility device. "The fluid proposed by Ji-Ping Huang of Fudan University in Shanghai, China, and colleagues, contains magnetite balls 10 nanometers in diameter, coated with a 5-nanometer-thick layer of silver, possibly with polymer chains attached to keep them from clumping. In the absence of a magnetic field, such nanoparticles would simply float around in the water, but if a field were introduced, the particles would self-assemble into chains whose lengths depend on the strength of the field, and which can also attract one another to form thicker columns. The chains and columns would lie along the direction of the magnetic field. If they were oriented vertically in a pool of water, light striking the surface would refract negatively – bent in way that no natural material can manage."

We already have those. I change channels on TV with them every night. And, be damned if you're going to take my magic stick away from me. Taking it away is like taking food from an angry dog. I don't care if you don't want to watch the Mystery Science Theater marathon, *I* have the magic stick!

We need some disambiguation, though. My "magic stick" seems to be very different than your "magic stick". Yours is likely black or silver; mine varies from light tan/pink to purplish. I'm sure there are other differences as well.

As a matter of fact, my "magic stick" is superior to yours, since I can cede control of it to my wife and still watch MST3K marathons.

I think I understand your confusion. But it's not exactly appropriate to call Mjollnir (Thor's Hammer), a "magic stick". That's like calling a lightning bolt sent from high above Mount Olympus by Zeus just a "pretty light".

Actually no, just the fact of being invisible. In order to be invisible you have to refract all the light that would normally hit the object being invisible, meaning it would be in absolute dark. You could be invisible in the girls (or guys for the/.ers so persueded) shower room, but you couldn't see a blasted thing. Any lighted object within the cloak could also, possibly, leak out giving away your concealment. So even IF (a big if) the use of, say, an infrared camera, would allow you to see through

Maybe sensational reporting of just about everything (eg the LHC) is causing the public's lack of affinity for science. All they see is hundreds of 'broken promises' made by the media about fantastic whizz-bang technologies that the research

A good thing too , otherwise there wouldn't be any inventions.The problem is , just an idea isn't good enough : you need a plan to put it into practice , and you need money in order to bring it into a workable product.

That means you have to find investors, and 'Liquid Invisibility Cloak' sells better than 'Theoretical material with exotic optical effect' .

I can understand how they could use these materials (theoretically anyway) to make Julian Beever-style illusions (see http://www.moillusions.com/2007/12/julian-beevers-new-3d-sidewalk.htm [moillusions.com]). But a real invisibility cloak has to detect the direction of every photon striking it and deliver that proton in the same direction out the exact opposite side of the cloak, doesn't it? Otherwise the effect is likely to be like a Beever painting, viewable from only one precise viewpoint.

you're missing the point. this is more of a lens. It redirects light around the object. now, how fluidly it does this has yet to be seen, but any light that originates behind the object will be bent in a way that it never strikes the object. I'm not sure how this would look in real life, but given a mathmatically perfect lens, the object would bend all light around it so that it comes out exactly on the other side. In that case, as far as our sense of sight is concerned, the object would not exist

And as far as it's sense of sight is concerned, the rest of the world would not exist.

Ever heard of view-holes? We only need about a quarter-inch diameter hole to get a nearly 180 degree field of view. Cameras can do the exact same thing, often times with less.

I don't know if you know this, but it's a lot harder to see a little dot a quarter-inch in diameter floating in space than it is to see a 6' tall person or a 10' by 15' tank, or whatever the hell ends up getting cloaked.

Taking care of visibility out is downright EASY. You simply need a very small (in size) light collector just outsi

They are talking about a material that has a negative refractive index when placed under a magnetic field. If it has a negative refractive index for all wavelengths of visible light, then it IS an invisibility cloak. They aren't talking about transmitting light through the object, as you seem to think, but rather bending light AROUND it, which is possible and does work (at certain wavelengths).

All metamaterials are not created equal. A metamaterial is an electromagnetic medium created by a composite of tiny (very subwavelength) constituent structures, put together in such away that longer wavelengths see an "average" material with properties very different from those of the constituents. Usually, the goal is to use resonant effects in the microscopic constituents to make a material that is effectively very different from naturally occuring EM media. But this can be done for many different purposes.

A negative-refractive metamaterial is designed to have an effective "negative" index of refraction, which makes Snell's law (refraction) bend backwards, and can potentially be used for flat-lens near-field imaging, subwavelength imaging (again only in the near field), etcetera. The main practical difficulty here is that the most interesting applications of negative-index materials are in the visible or infrared regime, but negative-index metamaterials rely on metallic constitutents and metals become very lossy at those wavelengths.

Recent "invisibility" cloak proposals are based on the observation that there is a one-to-one mapping between transforming space to "curve around" the object being cloaked and keeping space the same and transforming the materials. So, if you can make materials with certain properties, they could effectively cloak an object by causing all the light rays to curve around the object just as if space were curved. Although this is mathematically quite beautiful, there are many practical obstacles to making this a reality. The proposal is to make the required materials via metamaterials, but these are NOT negative-index metamaterials. The required materials theoretically tend to require some singularities (points where the index blows up or vanishes), and trying to approximate that in practice inevitably involves losses which spoil the cloaking. In general, the bigger the object to be cloaked compared to the wavelength, the smaller the losses have to be, and the narrower the bandwidth is going to be. When you work out the numbers, you see that this is why all the experimental demonstrations of cloaking have only "cloaked" (reduced the scattering crosssection, but not to zero) objects that were a wavelength or two in diameter. Cloaking macroscopic objects at visible wavelengths is a fantasy because the material requirements are insane. The only remotely practical prospects seem to be cloaking objects on the ground (which makes things technically easier because the coordinate transformations are nonsingular) to long-wavelength radiation, e.g. cloaking something against radio waves.

Finally a use for transparent ferro-fluids http://www.youtube.com/watch?v=me5Zzm2TXh4 [youtube.com] ? I wish TFA had a better description of how this is supposed to work, so I will have to resort to some serious hand-waving: It sounds like they are trying to make field-aligned wave guides. This would be similar to the way our magnetosphere moves plasma from the night side to the day side by moving around the Earth's magnetic field, a process that happens whenever the magnetic field of the solar wind points south. The ana

Well, besides not being fictional, the big idea is that the thing (potentially) has a negative index of refraction, something not even the fictional lenses do.

Negative refraction is useful in making invisibility shields, by directing light completely around object surrounded by it.

This doesn't go nearly that far; it's a step towards a new way of constructing metamaterials with negative indexes. That's important; the "invisibility" stuff is just press-release science because invisibility is far more interes

An internal power source must obey the laws of thermodynamics and thus would cause the craft as a whole to be an infrared emitter. We are very good at detecting infrared light which would defeat most cloaking devices including this one.

It would work "optically" if the Invisibility Cloak was made out of vegetable oil and you were made of Pyrex...

Vegetable oil and Pyrex has the same refractive index...

* put a small Pyrex jar into a larger one and then fill the smaller (inner) jar with vegetable oil and once it's full continue to fill the larger one with the overflow. The smaller (inner) jar will become invisible, to the naked eye.

On a more serious note this seems to be a big problem with all invisibility cloaks, of non supernatural origin (calm down HP fans), and that is they are all based upon modifying materials refractive index and thus bending the light around the object you want to hide.

That all sounds good but if you could do this to hide an object; If that object were a person since light doesn't hit them, or their eyes, not only would they be invisible but they would also be blind. I think most people asking Santa for a invisibility cloak would like to actually see what's in the girls locker room right?

A perfect invisibility cloak would change the person wearing it, along with the cloak, to a refractive index of air but again, they would be perfectly blinded by the process. In the case of RI = air then the light would go straight through them, included their eyes. So you either bend the light or have it go through your eyes and either way your in the dark.

I guess you could hide everything but your pupils, but in my book you wouldn't be invisible then, floating eyeball freak!

And this is exactly why a proper invisibility cloak must be computer controlled with millions of dots of resolution interspersed with millions of cameras. The idea is that, like a chameleon, you change to look like your background. With you inside, the cameras can also give you a view of your surroundings.

And yes, it would still give off a heat signature, but most people aren't walking around with night vision goggles all the time.

An invisibility cloak, as in the sort used by harry potter, is not possible with a passive device. This is fairly obvious since you can't see light and yet be transparent to it at the same time.

However, there is no theoretical limit if the device is active. A simple example would be a flat panel display with a camera on the back. If you track the position of the observer, you can create a very convincing "invisibility" effect.

More interestingly, it may one day be possible to use active metamaterials to prod

Granted, as soon as you poke a camera out of the field it isn't 100% invisible, it's only 99.99% (or more) invisible. Still that's pretty damn good, do you know how hard it would be to notice a tiny dot floating around in space?